Electric contact device



Oct. 20, 1964 A. KRAEMER 3,153,709

ELECTRIC CONTACT DEVICE Filed Sept. 29, 1960 5 Sheets-Sheet l Oct. 20, 1964 A. KRAEMER ELECTRIC CONTACT DEVICE 5 Sheets-Sheet 2 Filed Sept. 29. 1960 Oct. 20, 1964 A. KRAEMER 3,153,709

ELECTRIC CONTACT DEVICE Filed Sept. 29. 1960 3 Sheets-Sheet 3 United States Patent 3,153,709 ELECTRIC CONTACT DEVICE Asger Kraemer, Nordborg, Denmark, assignor to Danfoss ved ingenior Mads Clausen, Nordborg, Denmark Filed Sept. 29, 1960, Ser. No. 59,281 Claims priority, application Denmark, Sept. 29, 1959, 3,477/59 2 Claims. (Cl. 200-84) The invention relates to an electric contact device, preferably for controlling the water level in boilers or similar tanks for water or liquid, and having two electric switches which cooperate with a control member movable in accordance with the level on the water or liquid.

Electric control devices of the aforesaid kind are known, but they have the drawback that it is Only with difficulty and with the use of special tools that they can be adjusted to respond at fixed values of the water level.

It is the object of the present invention to devise an electric contact device of the aforesaid kind in which the above-mentioned type of adjustment can be effected in a simple manner so that the water levels at which the contact device responds, for example for starting or stopping a rotary pump connected with the liquid tank or for acting on an alarm device to indicate a too high or a too low water level may be determined beforehand and with relatively great accuracy.

An essential feature of an electric contact device according to the invention is that between the control member and the actuating means of the two switches there is inserted a pivotable, two-armed tilting bridge whose two arms in the neutral position of the tilting bridge are disposed resting in contact with the actuating member of each of the switches, the tilting bridge being provided with holder arms which at adjustable clearances engage the control member.

The result obtained is that in an extreme value of the clearance one holder arm determines at which water level the tilting arm is to act upon one switch, for example for starting or stopping the motor pump which feeds water or liquid to the tank, whereas the other holder arm determines at which water level the tilting arm in another extreme value of the clearance the tilting arm is to act on the other switch, for example for rendering an alarm effective to indicate lowest permissible or highest permissible level of water or liquid. Another result obtained is that the difference between the two levels of water or liquid may be altered to suit requirements, since the clearance is adjustable.

In one embodiment of the electric contact device according to the invention each switch has a stable position and an unstable position and the tilting bridge is provided with a pressure spring so dimensioned and disposed that it acts on the tilting bridge biasing it to at a bias which is capable of retaining one of the switches in its unstable position in which the bias is insufficient to operate the switch from its stable into its unstable position.

The result obtained is a substantial reduction in the number of starts and stops of the motor pump since the motor only starts when the water level has sunk so much that the contr l member and the other holder arm actuate the tilting bridge into a position in which it acts upon the other switch.

In another embodiment of the contact device according to the invention the pressure spring rests against an adjustable rest for changing the momentum exerted by the pressure spring on the tilting bridge.

The result obtained is that the pressure spring can be adjusted to provide the tilting bridge with such a bias against the actuating member of the first switch that the actuating member remains depressed until the control member acts on the other holder arm.

3,153,709 Patented Oct. 20, 1964 In a third embodiment of the contact device according to the invention the holder arms are pivotably mounted in the tilting bridge about a pivot thereof. A spring is disposed around the shaft forcing the ends of holder arm which are remote from the tilting bridge away from each other, while an adjustment arm, pivotably mounted in the tilting bridge, has webs limiting the clearance of the holder arms.

As a result, the distance between the two holder arms and consequently the movement area of the control member between the two extreme positions, in which the control member acts upon the holder arms, can be varied.

The invention will now be further described with reference to the drawing, in which:

FIGURE 1 is a side view of an electric contact device according to the invention,

FIGURE 2 is an end view of same,

FIGURE 3 is the same, viewed from below,

FIGURE 4 is a detail of the contact device according to the invention,

FIGURE 5 is an exploded view of an adjustment arm arrangement for the contact device shown in FIGURE 4,

FIGURE 6 is a perspective view of the contact device, the switches incorporated in the device being removed, and the device being seen in oblique direction from above,

FIGURE 7 is the same, viewed in oblique direction from below, 7

FIGURE 8 is a diagram showing the mode of operation of the contact device, and

FIG. 9 is a side elevation view of a tank partly in section to which a switch according to the invention is operably connected for water level control therein.

In the drawing, m and M are electric switches of the micro-switch type with pressure pins, 1 and T, respectively, adapted to change the movable contacts of the switches from their closed to their open positions, or conversely. The switches m: and M are mounted in a frame 1 and retained by through-bolts 2 with nuts 3. The switches have contacts (not shown), viz. two fixed and one movable, connected with outer terminals 4, 5 and 6, and the switches are of snap-action type so that in the most advanced position of the pressure pins, t and T, respectively, the terminal 6 may be connected with the terminal 4, while in the depressed position of the pressure pin the terminal 6 may be connected to the terminal 5. The two switches m. and M are so disposed in the frame 1 that a two-armed tilting bridge 7 tilting about its pivot pin 8 to which it is connected by webs 9 may be caused to depress the pressure pins, either t or T, each of which is located opposite a respective one of its separate arms, 10 or 11. The two arms are located on either side of the rotational shaft or pin 8. Each of the switche has a stable position, viz. in the most advanced position of the pressure pin, and an unstable position in the depressed position of the pressure pin. The tilting bridge is so disposed that in its neutral position it rests in contact with both pressure pins without exerting any essential pressure on the pins; in its neutral position, the tilting bridge may, for example, be at a distance of a few tenths of a millimetre from the pins. In the neutral position of the tilting bridge as shown in FIGURE 1 the pressure pins are therefore in their advanced position in which the terminal 6 is in connection with the terminal 4, but interrupted from the terminal 5. The tilting bridge 7 can be brought into its two extreme positions in which the pressure pins 1 and T respectively are depressed by means of holder arms 12 and 13 which are pivotable about the rotational shaft 8 of the bridge 7, such parts 14 and 15 of the said arms as are within shorter distance of the tilting bridge resting against edges 16 and 17, respectively, of an adjustment arm 18 under the action exerted by a spring 19 which is mounted on the rotational shaft 8 and forces such outer ends 20 and 21 of the holder arms as are remote from the tilting bridge 7 from each other. The adjustment arm 18, illustrated in FIGURE as viewed from the front of the contact device, is pivotably mounted about a pivot 22 provided in the tilting bridge 7, and such end of the arm 18 as is remote from the pin 22 is provided with an adjustment handle 23. The movement of the adjustment arm 18 about the pivot 22 is limited by a slit 24 provided in the tilting bridge 7, a screw 25 provided on the adjustment arm being moved through the slit 24-. When the adjustment arm lid is moved towards one of its extreme positions which is limited by one end of the slit 24, the edges 16 and 17 are turned in such manner that the end 29 and 21 of the holder arms are forced from each other; if the adjustment arm is passed towards its other extreme position which is limited by the other end of the slit 24, the ends 20 and 21 of the holder arm will approach each other.

If the contact device is to be used as shown in FIG. 9 for controlling the water level in a receptacle or a tank 30 for water or other liquid, it is placed in such manner that the outer ends 20 and 21 of the holder arms 12 and 13 by a clearance determined by the position of the holder arms in relation to each other seize a control member such as one end of a two-armed lever 31 moved by variations in the water or liquid level. The other end of said lever is connected to e.g. a float 32 moving in accordance with the variations in the level of water contained in the tank. The two-armed lever may be pivotably mounted in the wall of the tank or extend through a diaphragm built in the wall. When the water level varies, the lever will thus turn about a horizontal axis 33 and in a vertical plane and the electric contact device is mounted in such manner in relation to the lever that the rotational shaft 8 is disposed at right angles to the vertical plane. The lever 31 is provided with a free tip 34 projecting to a point between the free ends 20 and 21 of the holder arms 12 and 13. At a high water level in the tank as indicated in a diagram in FIGURE 8 at a point N at an axis h of the ordinate, the tip of the lever will rest against the free end 20 of the holder arm 12 and thereby positively force the tilting bridge 7 against the pressure pin t of the switch m. If an electromotor (not shown) coupled to a pump for supplying water to the tank is connected to a voltage generator across the terminals 4 and 6 the pressure pin I will be in its depressed position and the motor will not receive current. If, however, the water level in the tank is low as shown in FIG. 9 and indicated in FIGURE 8 at a point N of the same axis h of the ordinate, the lever will rest against the free end 21 of the holder arm 13 and thereby force the tilting bridge 7 heavily against the pressure pin T of the switch M. If an alarm device (not shown) is connected to an electric circuit across the terminals 5 and 6 of the switch M, the alarm device will receive current and alarm to indicate a too low water level in the tank. On the other axis g of the ordinate with a graduation corresponding to h is indicated the position of the free tip of the said lever, for example at a point S corresponding to the level N and S corresponding to the level N At points S and S is indicated the position of the said tip when the declining water level has reached the level N or a level N, which is characterised thereby that the said tip loses contact with the extreme end 20 of the holder arm 12 and establishes contact with the extreme end 21 of the holder arm 13. The distance 8 -8 corresponds thus to the travel of the said tip between the holder arm ends 20 and 21 in a gap which in FIGURE 6 is indicated by the reference numeral 26 where the tip of the control member must be assumed to move in a plane at right angles to the rotational shaft 8. As long as the tip is moving between the ends 20 and 21 of the two holder arms, the tilting bridge 7 will be in its neutral position and the pressure pins 2 and T be in their advanced position, that is, the switch m has closed the electric circuit to the motor pump across the terminals 4, 6, whereas the switch M has interrupted the connection to the alarm device across the terminals 5, 6, so that the pump is working and there is no alarm. It will be appreciated that the difference between the two levels N and N, can be varied by turning the adjustment arm 18 which by means of the edges 16, 17 force the ends 29 and 21 more or less from each other. If the level falls from N to N the pressure pin t of the switch in will move from its depressed position which the electrical connection between the terminals 4, 6 is interrupted and the pump consequently at a standstill, to its advanced position, in which the electrical connection between the terminals 4 and 6 is established, that is, the motor pump is started. At an intermediate level N the switch will be cut in and at this level the pump motor starts.

By means of lines I and L in connection with the axis of abscissa of FIGURE 7 are graphically indicated the movements of the pressure pins t and T, respectively, when the pressure pin moves from the point S to S and from the point 5. to the point S respectively a switch of the micro-switch type as those shown having as known an advance movement 1, an after movement e and a difierential movement D as indicated in FIGURE 8 for the switch m. The corresponding movements of the switch M are indicated by the letters F, E and D, respectively, that is when the switch m in the depressed position of pressure pin t at the level N is moving outward at declining water level, the switch m will close the circuit for the pump motor at a point b corresponding to the level N whereas at rising water level it only breaks at point a, corresponding to a higher level N This is illustrated graphically in FIG- URE 8 by an axis p of the ordinates, in which a shaded area v to the left of the axis p of the ordinates indicates current to the pump motor at declining water level, whereas another shaded area v to the right of the said axis of the ordinates indicates current to the pump motor at rising water level. The corresponding constants for the switch M are denoted correspondingly, but in capital letters B, A and V and V as indicated on another axis (P of the ordinates.

As appears from FIGURE 7, the switch M will close the circuit for the alarm device at a level N in case of falling water level, which level is higher than a level N at which the switch breaks the current for the alarm device.

The mode of operation of the contact device is as follows:

At a water level N in the tank both the switch m and the switch M are in their interrupted position, that is, the motor pump is stopped and the alarm device cut out. As the quantity of water or liquid is used, the level in the tank falls, and at the level N the motor pump starts and feeds water or other liquid to the tank. If the consumption exceeds what corresponds to the capacity of the pump, the level will continue falling, and at the level N the switch M closes the circuit for the alarm device. If the consumption is only for a short time exceeding what corresponds the pump capacity the quantity of water fed will exceed the quantity of water consumed, and the level rises until the level N is reached, when the switch in cuts out the pump. If, however, the consumption for a certain interval of time is varying around an amount corresponding to the capacity of the pump, the level will vary between the values N and N which involves many starts and stops of the motor thereby subjecting the contacts of the device as well as the motor to undue wear, and the motor is simultaneously exposed to excessive heat since it is left no time for cooling during the intervals between stops and starts.

To remedy this drawback effective measures may be taken as each of the switches m and M according to the invention has a stable position in which its pressure pin t or T is in its advanced position and an unstable position in which the pressure pin of the switch is in its depressed position and the tilting bridge 7 is provided with a pressure spring 27 so dimensioned and disposed by means of a rivet 27a on the tilting bridge 7 that it acts on the latter at a bias which is capable of retaining the switch m in its unstable position, but insuflicient to change the switch m from its stable to its unstable position. According to the invention this bias is obtained thereby that the pressure spring 27 is resting against an adjustable rest such as a screw 28 retained by screwthreads in the frame 1 and secured by a lock nut 29 after being set so as to ensure the required bias. The switch in will in that case only close the circuit for the motor pump when the water level has fallen to the level N since the tip of the control member (not shown) only then in the position 8,, has moved to contact the extreme end 21 of the holder arm 13, after which the pressure pin t is relieved of the pressure exerted by the tilting arm 7 and moves into its advanced position in which the switch 111' closes the circuit for the pump motor. This is illustrated graphically on an axis (g of the ordinates in which the shaded areas W and W represent the two areas in which the switch m is closed during declining and rising level, respectively.

The operation of the last mentioned embodiment of the contact device is as follows:

As long as the water level is falling from the level N to the level N the switch in is in its open position, its pressure pin t being in its depressed position and the motor pump accordingly disconnected but at the level N the switch M will close a circuit for the pump motor and this will start and the pump will deliver water to the tank. If the capacity of the pump is sufiicient to supply a quantity of water exceeding the consumption during the subsequent interval of time, the level will rise to the level N at which point the switch m again switches off the motor, which will consequently make fewer starts and stops so that the wear on the contacts of the switch in is substantially reduced.

It will be appreciated that the pressure spring 27 has no essential influence on the mode of operation of the switch M, even though the pressure spring 27 cooperates to tilt the tilting bridge 7 away from contact with the pressure pin of the switch M.

It will further be appreciated that the pressure spring 27 does not alter the possibility of increasing or reducing the difference between the points and 8,, by means of the adjustment arm 18. By turning the said adjustment arm not only the points S and 8,, will be displaced towards or away from each other, but at the same time the points S and S will be displaced correspondingly, that is, the difference between the levels N and N can be varied by means of the adjustment arm 18 with relatively wide limits and thereby adapt the quantity of reserve water in the tank to a predetermined average consumption.

What I claim and desire to secure by Letters Patent:

1. An electric contact device, for controlling a liquid level in boilers, tanks for water or other liquids and the like, comprising two electric switches each having actuating means biased to an operative position corresponding to a stable position and having an unstable position corresponding to another operative position of each respective switch, a control member movable in response to changes of the level of a liquid for controllably actuating said switch actuating means, a pivotable, two-arm tilting bridge having two arms operative to a neutral position of said tilting bridge in which each arm rests in a position for activating respective ones of said actuating means of said switches from said stable position to said unstable position, said neutral position corresponding to a selected liquid level, means for rocking said tilting bridge under control of said control member comprising holder arms for receiving said control member therebetween, means biasing said holder arms toward each other at adjustable spaced apart positions relative to each other and in position to be engaged by said control member alternatively to rotate said bridge from said neutral position and back to said neutral position in response to said control memher for actuating said switches alternatively in dependence upon the direction and extent of movement of said control member, a pivot pivotally mounting said bridge, means mounting said holder arms pivotally relative to said tilting bridge to pivot about the rotational pivot of said bridge, said holder arms having free end portions comprising portions on said arms spaced the farthest from said bridge and having free ends, said biasing means being disposed for biasing said free ends toward each other, adjustable means for adjustably setting said free ends of the holder arms in spaced apart positions from each other and to variably and accurately determine said spaced apart positions and a clearance between said free ends, and said control member being disposed between said free ends to engage said free ends alternatively in dependence upon its direction of movement and extent of movement and the clearance set between said control member and said free ends.

2. An electric contact device, for controlling a liquid level in boilers, tanks for water or other liquids and the like, comprising two electric switches each having actuating means biased to an operative position corresponding to a stable position and having an unstable position corresponding to another operative position of each respective switch, a control member movable in response to changes f the level of the water or liquid for controllably actuating said switch actuating means, a pivotable, two-arm tilting bridge having two arms operative to a neutral position of said tilting bridge in which each arm rests in a position for activating said actuating means of said switches from said stable position to said unstable position, said neutral position corresponding to a selected liquid level, means biasing said bridge to an operative position in which one of said arms engages one of said activating means and partially displaces it toward said unstable position and away from said stable position, means for rocking said tilting bridge under control of said control member comprising holder arms for receiving said control member therebetween, means biasing said holder arms toward each other at adjustable spaced apart positions relative to each other and in poistion to be engaged by said control member alternatively to rotate said bridge from said neutral position and back to said neutral position in response to said control member for actuating said switches alternatively in dependence upon the direction and extent of movement of said control member, a pivot pivotally mounting said bridge, means mounting said holder arms pivotally relative to said tilting bridge to pivot about the rotational pivot of said bridge, said holder arms having free end portions comprising portions on said arms spaced the farthest from said bridge and having free ends, said holder arms biasing means being disposed for biasing said free ends toward each other, adjustable means comprising an adjusting arm for adjustably setting said free ends of the holder arms in a multiplicity of spaced apart positions from each other and to variably and accurately determine said spaced apart positions and a clearance between said free ends, and said control member being disposed between said free ends to engage said free ends alternatively in dependence upon its direction of movement and extent of movement and the clearance set between said control member and said free ends.

References Cited in the file of this patent UNITED STATES PATENTS 744,817 Sundh Nov. 24, 1903 877,790 Mintz Jan. 28, 1908 1,854,540 Carlson Apr. 19, 1932 2,511,271 Kaminky et a1 June 13, 1950 2,721,915 Huntley Oct. 25, 1955 2,748,220 Lung May 29, 1956 2,774,058 Raichel Dec. 11, 1956 2,801,308 Cubellis July 30, 1957 2,904,652 Crane et al Sept. 15, 1959 

1. AN ELECTRIC CONTACT DEVICE, FOR CONTROLLING A LIQUID LEVEL IN BOILERS, TANKS FOR WATER OR OTHER LIQUIDS AND THE LIKE, COMPRISING TWO ELECTRIC SWITCHES EACH HAVING ACTUATING MEANS BIASED TO AN OPERATIVE POSITION CORRESPONDING TO A STABLE POSITION AND HAVING AN UNSTABLE POSITION CORRESPONDING TO ANOTHER OPERATIVE POSITION OF EACH RESPECTIVE SWITCH, A CONTROL MEMBER MOVABLE IN RESPONSE TO CHANGES OF THE LEVEL OF A LIQUID FOR CONTROLLABLY ACTUATING SAID SWITCH ACTUATING MEANS, A PIVOTABLE, TWO-ARM TILTING BRIDGE HAVING TWO ARMS OPERATIVE TO A NEUTRAL POSITION OF SAID TILTING BRIDGE IN WHICH EACH ARM RESTS IN A POSITION FOR ACTIVATING RESPECTIVE ONES OF SAID ACTUATING MEANS OF SAID SWITCHES FROM SAID STABLE POSITION TO SAID UNSTABLE POSITION, SAID NEUTRAL POSITION CORRESPONDING TO A SELECTED LIQUID LEVEL, MEANS FOR ROCKING SAID TILTING BRIDGE UNDER CONTROL OF SAID CONTROL MEMBER COMPRISING HOLDER ARMS FOR RECEIVING SAID CONTROL MEMBER THEREBETWEEN, MEANS BIASING SAID HOLDER ARMS TOWARD EACH OTHER AT ADJUSTABLE SPACED APART POSITIONS RELATIVE TO EACH OTHER AND IN POSITION TO BE ENGAGED BY SAID CONTROL MEMBER ALTERNATIVELY TO ROTATE SAID BRIDGE FROM SAID NEUTRAL POSITION AND BACK TO SAID NEUTRAL POSITION IN RESPONSE TO SAID CONTROL MEMBER FOR ACTUATING SAID SWITCHES ALTERNATIVELY IN DEPENDENCE UPON THE DIRECTION AND EXTENT OF MOVEMENT OF SAID CONTROL MEMBER, A PIVOT PIVOTALLY MOUNTING SAID BRIDGE, MEANS MOUNTING SAID HOLDER ARMS PIVOTALLY RELATIVE TO SAID TILTING BRIDGE TO PIVOT ABOUT THE ROTATIONAL PIVOT OF SAID BRIDGE, SAID HOLDER ARMS HAVING FREE END PORTIONS COMPRISING PORTIONS ON SAID ARMS SPACED THE FARTHEST FROM SAID BRIDGE AND HAVING FREE ENDS, SAID BIASING MEANS BEING DISPOSED FOR BIASING SAID FREE ENDS TOWARD EACH OTHER, ADJUSTABLE MEANS FOR ADJUSTABLY SETTING SAID FREE ENDS OF THE HOLDER ARMS IN SPACED APART POSITIONS FROM EACH OTHER AND TO VARIABLY AND ACCURATELY DETERMINE SAID SPACED APART POSITIONS AND A CLEARANCE BETWEEN SAID FREE ENDS, AND SAID CONTROL MEMBER BEING DISPOSED BETWEEN SAID FREE ENDS TO ENGAGE SAID FREE ENDS ALTERNATIVELY IN DEPENDENCE UPON ITS DIRECTION OF MOVEMENT AND EXTENT OF MOVEMENT AND THE CLEARANCE SET BETWEEN SAID CONTROL MEMBER AND SAID FREE ENDS. 